1. Field of the Invention
The present invention relates to a polymerizable ester compound, particularly useful as a starting material for a functional material. Further, the present invention relates to a polymer having a repeating unit derived from the polymerizable ester compound, a photoresist material containing the polymer, and a patterning process using the photoresist material.
2. Description of the Related Art
In recent years, efforts have been made to achieve a finer pattern rule with increased integration and processing speeds in LSI devices. Deep-ultraviolet lithography has been developed as a technique capable of achieving microfabrication of 0.3 μm or less. In particular, a technique using a KrF excimer laser light has been completely known as an industrially production process.
Chemically amplified resist materials for use in photolithography using an ArF excimer laser light with a wavelength of 193 nm as a light source are, of course, required to have a high transparency in the wavelength. Further, they are required to have a high etching resistance enough to allow for film thickness reduction, a high sensitivity enough to avoid any burden on an expensive optical material, and especially a high resolution enough to form a precise micropattern. In order to meet these requirements, it is necessary to develop a base resin having a high transparency, rigidity, and reactivity. Such a base resin has been actively developed.
As a resin highly transparent to an ArF excimer laser light, a copolymer of acrylic or methacrylic acid derivatives (see Patent Document 1) has been known.
As disclosed in Patent Document 2, a combination of a (meth)acrylic unit having a methyladamantane ester as an acid labile group unit with a (meth)acrylic unit having a lactone ring ester as an adhesion group unit has been proposed as a (meth)acrylic resin. Patent Document 3 has described an acid labile group of exo form. The group has a high deprotection reactivity and a low activation energy for deprotection reaction. For this reason, it can obtain a high resolution and a low dependence on post exposure bake (PEB). Norbornane lactone as disclosed in Patent Documents 4 and 5 has been also proposed as an adhesion group having enhanced etching resistance. Patent Document 6 has described a specific compound having a high fluorine content and a hydroxy group. These studies have achieved significant improvements in the resolution of ArF resists.
However, from the conventional materials, a micropattern having a pitch less than 200 nm is unlikely to be formed, and additionally is not a complete rectangle. Further, the pattern has very rough surfaces and side walls. Therefore, the pattern does not reach a practically acceptable level. Among the problems of the conventional materials, there is the most serious problem of roughness in fine line size (line edge roughness). The problem largely affects the performance of a produced semiconductor device. Therefore, it is necessary to solve the problem. A smooth pattern can be simply formed by using a resin having a lower molecular weight or making an acid generated by a photoacid generator easy to move. Thus, the object can be accomplished to some extent. However, characteristics such as exposure dose dependence, density dependence, and mask fidelity extremely deteriorate, and fine fluctuation of a mask enlarges to make the line size uniform. As a result, line edge roughness does not reduce. In order to cope with a finer pattern of ArF excimer laser lithography and a high resolution by using an immersion lithography process, a fundamental improvement of line edge roughness is required.